In today's perpendicular magnetic recording (PMR) technology, an all wrapped around (AWA) shield writer is widely used by the major hard disk drive (HDD) manufacturers. The function of a trailing shield in an AWA structure is to improve the magnetic field gradient along a down track direction which is a key requirement for high bits per inch (BPI). Meanwhile, side shields and a leading shield serve to define a narrower writer bubble which is important for realizing higher tracks per inch (TPI). In order to achieve higher area density (i.e. higher BPI and TPI) in advanced writer designs, the gap between the main pole and all shields, including the write gap adjoining the trailing shield, side gaps to the side shields, and lead gap next to the leading shield must be as narrow as possible. However, the material used for conventional AWA shields is a soft magnetic material without preferred anisotropy. Therefore, narrowing the gap between a shield and main pole will only lead to an unwanted flux path from the main pole to the shield which in turn reduces the writability (magnetic field) of the writer on magnetic recording media. This dilemma is considered one of the most significant challenges to improving current writer designs and performance.
Referring to FIG. 1, internal flux loss is depicted in a conventional PMR writer 1 comprising a main pole 11 and shield 12 that can represent a trailing shield, side shield, or leading shield depending on the direction of movement of the writer over magnetic medium 10 during a write process. Magnetic charges 7a, 8a of opposite sign are shown on an air bearing surface (ABS) side of the shield 12, and main pole 11, respectively, and are responsible during a write process for the preferred direction 5 of flux Bs1 from the main pole to the magnetic medium, and returning from the magnetic medium to the shield. Magnetic flux Bs0 is provided to the main pole from coils (not shown). As the gap (distance) between main pole and shield becomes smaller, flux loss Bs2 in a direction 6 from main pole to shield becomes more severe due to magnetic charges 7b, 8b on opposing sides of the shield, and main pole, respectively. Consequently, the write field Bs1 on the magnetic recording medium will be degraded. With the constraint of write field amplitude on the magnetic medium 10, further reduction of the gap between main pole and shields is not productive which limits achieving a higher recording area density. In particular, decreasing the write gap between main pole and trailing shield has been an effective way in improving field gradient and BPI during the past few years. However, current technology does not enable further field gradient improvement when the write gap shrinks below 20 nm. One possible reason is the magnetic charges 7b, 8b for main pole and trailing shield are more concentrated on opposing sides as pictured in FIG. 1 than on the ABS surface when the write gap becomes too narrow in conventional designs. Thus, an improved writer design is needed to minimize flux loss Bs2 and maximize write field Bs1.
A search of the prior art revealed the following references. U.S. Patent Application 2010/0157484 shows a magnetic field auxiliary pole and a non-magnetic layer stacked on the main pole to increase field strength and gradient. However, the stacked layers are recessed from the ABS and are not expected to entirely prevent flux leakage from the main pole to an adjacent trailing shield.
In U.S. Patent Application 2010/0149697, a trailing shield is shown with multiple layers and is separated from the trailing side of a main pole by a gap layer.
U.S. Pat. No. 7,657,992 discloses a small trailing shield stitched onto the main pole at the ABS but separated from the main pole by a write gap layer.
U.S. Pat. No. 6,530,141 describes a magnetic pole construction resulting in a high field gradient.
A. Hashimoto et al. describe the use of a negative Ku magnetic material in “A soft magnetic underlayer with negative uniaxial magnetocrystalline anisotropy for suppression of spike noise and wide adjacent track erasure in perpendicular magnetic recording media”, Journal of Applied Physics, 99, 08Q907 (2006).
A composite grain of easy plane material (CoIr with negative Ku) and perpendicular anisotropy material (CoPt with positive Ku) are used in a magnetic medium to improve the head field gradient and amplitude as described by Park et al in “A novel crystalline soft magnetic intermediate layer for perpendicular recording media”, Journal of Applied Physics, 105, 07B723 (2009), and in “Co-7% Ir Soft Magnetic Intermediate Layer for Perpendicular Media”, IEEE Transactions on Magnetics, Vol. 46, No. 6, June 2010.
Takahashi et al. discuss structural and magnetic analyses of a′-Fe—C films in “Magnetocrystalline Anisotropy for a′-Fe—C and a′-Fe—N Films”, IEEE Transactions on Magnetics, Vol. 37, No. 4, July 2001.